According to the complaint, filed with the New York State Supreme Court, the harassment began slightly over a year ago. At one point, Mr. Charney alleges in his complaint, a partner named Eric Krautheimer tossed a document at Mr. Charney’s feet and said “bend over and pick it up—I’m sure you like that.”

Mr. Krautheimer declined to comment on the accusation, and referred The Observer to the coordinator of the august firm’s labor and employment practice, Theodore Rogers.

He in turn referred to a statement issued via e-mail by the firm that reads, in part: “The Firm categorically denies Mr. Charney’s allegations of discrimination and retaliation.”

There have been other discrimination complaints filed by gay lawyers against big firms: complaints about benefits for same-sex couples, or alleging sexual advances made by superiors in the workplace. But Mr. Charney’s is different, painting a brutal picture of locker-room machismo in one of Manhattan’s most prominent firms.

Insiders say Sullivan & Cromwell is well known for its buttoned-up culture.

“Sullivan & Cromwell is a distinguished firm with a well-known reserved culture,” said Alisa Levin, a principal at legal recruiter Greene-Levin-Snyder. “I would never go to S&C in anything other than a proper skirt suit, whereas I would go to just about every other firm in edgy dress.”

But in a survey of law firms drawn from anonymous interviews and published on the Web site Vault.com, the entry for Sullivan & Cromwell reads, in part: “Regarding acceptance of gays and lesbians, “it’s unfair that Cleary has the gay-friendly rep,” says a contact, “because S&C is undoubtedly at least as supportive.” Sexual orientation is a non-issue, as Sullivan “has many outspokenly gay partners and associates who are fully integrated into the firm’s professional and social life.”

Sullivan & Cromwell is a monster mergers-and-acquisition firm, 125 years old and as blue-blooded and white-shoed as they come.

Its history stretches back to its involvement in the creation of the Edison General Electric Company and U.S. Steel; last year, for the third year in a row, Bloomberg News named the firm the top deal advisor for its role in counseling on $487.9 billion in transactions. Among those deals, S&C represented AT&T in its $83.1 billion buyout of BellSouth, the highest-valued deal in the world in 2006.

But even a firm that powerful doesn’t want to be tarred as retrograde in its treatment of gay associates. And as for Mr. Charney, if a trial does not vindicate him—well, what’s that line about getting work in this town again?

“These cases are rare because it’s the kiss of death to go sue a law firm,” said Leslie Corwin, a shareholder in Greenberg Traurig, who specializes in representing law firms. “It’s a tough thing to do if that’s the profession you want to be in.”

Perhaps unsurprisingly, that’s the reason Mr. Charney gives for the fact that he’ll be representing himself.

Mr. Charney said he called Lambda Legal Defense and Education Fund, a legal advocacy organization that represents gay clients on civil-rights-related issues, to aid in his case.

“I called the hotline, spoke to the representative who answered, and was told I would hear back from them,” he wrote in an e-mail. “Days later they returned my call and informed me that they were not interested in pursuing my matter against S&C.”

(A representative at Lambda contacted by The Observer said it does not comment on these matters.)

So in his free time, he wrote the complaint himself, walking it into the courthouse he had only visited twice before in his three and a half years as a lawyer, Tuesday morning.

After Mr. Charney scanned in the entire 25-page complaint and sent it out to members of the press, he said he received a call from the Mr. Rogers, informing him that he was being placed on leave from the firm while it conducted an investigation. His BlackBerry went dead.

“You just sometimes step back and realize that if you don’t do it no one else will,” said Mr. Charney, on the phone from the west midtown apartment where he’ll be spending a lot of his time. “This was a personal decision. You don’t plunge into taking on Sullivan & Cromwell by taking a straw poll.”

In his complaint, Mr. Charney alleges several instances in which partners and co-workers made derogatory remarks either directly to him or to others about him, dating from the fall of 2005. He is seeking punitive and compensatory damages.

In a statement e-mailed to firm members worldwide, its chairman, H. Rodgin Cohen, refuted Mr. Charney’s assertions. And he didn’t stop there.

“Mr. Charney first raised assertions of this sort in May 2006 through a lawyer, and his assertions were followed by a multi-million dollar demand,” wrote Mr. Cohen. Mr. Charney said the conversations, never got that specific. “I had an attorney and there were lots of conversations. There wasn’t anything that we were definitive about.”

In the meantime, Mr. Charney has no plans, other than attending to his own case.

“The day has been a real blur …. I’m in a rather uncertain state,” he said.

He says he loved his practice at Sullivan & Cromwell.

“I haven’t thought at all about what happens the day after this ends,” he said. “I’d like to be working at the firm still on my current clients. I didn’t ask to be removed today.”

Mr. Charney grew up in Syracuse, N.Y., and attended Brown University, graduating Phi Beta Kappa. He continued his education immediately following that at Columbia University Law School, earning honors as a Harlan Fiske Stone Scholar. Sullivan & Cromwell was his first choice of firms; as he puts it, rather worshipfully, “It’s probably the world’s most famous law firm. I felt fortunate to be there.”

But the complaint doesn’t make him look like a very lucky guy. In it, Mr. Charney accuses partners of obsessively pursuing information about the extent of his relationship with another associate (who is, according to the complaint, heterosexual). In the course of a performance review, the complaint alleges that one partner, James Morphy, told Mr. Charney that other partners had complained about his relationship and that it “need[ed] to stop.”

In other example, he refers to “documentation for circulation to all S&C partners in General Practice” circulated by another partner, Benjamin Stapleton III, that refers to Mr. Charney and this other associate as being “joined at the hip” and working “closely (too closely).”

In the complaint, he alleges that a partner, Alexandra Korry, described the relationship as “unnatural” to another co-worker.

(Mr. Morphy did not return a call for comment; Mr. Stapleton and Ms. Korry referred The Observer to Mr. Rogers.)

Mr. Charney describes in the complaint meeting with a partner to lodge a formal complaint of sexual-orientation discrimination, a fact corroborated by the Sullivan & Cromwell statement.

“The Firm promptly investigated his assertions at that time, and rejected Mr. Charney’s money demand,” wrote Mr. Cohen.

And yet he stayed at Sullivan & Cromwell, a fact that clearly had his employers confused.

“Mr. Charney chose to remain associated with the Firm thereafter.”

Mr. Charney’s complaint alleges that partner Stephen Kotran admitted that it had not been a “real investigation.”

(Mr. Kotran did not return a call for comment.) He says one partner, Ms. Korry, e-mailed the partner with whom he had lodged his complaint to call him “a liar.” He says he was excluded from a firm mentorship program and that an administrator admitted that the partner in charge was “sending a message.” He asserts that Mr. Rogers and Mr. Morphy fabricated a work evaluation of Mr. Charney, saying it was from Mr. Kotran. The report said that Mr. Charney and this other associate insisted on being staffed together, and that this closeness “could be grounds to ‘drive them out of the firm.’” Mr. Kotran disavowed the report.

By the end of the day, the link to Mr. Charney’s complaint on infirmation.com had been taken down, and in place of his morning posting, this comment: “The post that began this thread has been deleted, consistent with our policy against naming specific firm employees in a manner that may be harmful, threatening, abusive, harassing, tortious, defamatory, vulgar, obscene, libelous, invasive of another’s privacy, hateful, or racially, ethnically or otherwise objectionable, etc., etc.”